Glossary

A device used to measure the change in internal energy (ΔU) of a system at constant volume.

Bond enthalpy

The amount of enthalpy (or energy) needed to break one mole of a certain chemical bond.

Caloric

A precursor to the modern understanding of heat. Caloric was believed to be an invisible fluid capable of carrying heat.

Calorie

A unit of energy equal to the amount of energy needed to raise 1 gram of water by 1 degree Celsius.

Calorimeter

A device used to measure either the change in the internal energy or the change in enthalpy of a system.

Chemical energy

The energy of a system due to the arrangement and bonding of atoms.

Diesel engine

An internal-combustion engine in which the compression of fuel, not a spark plug, causes the fuel to ignite.

Electrical work

The work done on a charged particle by an electric field.

Endothermic

Absorbing heat from the surroundings.

Enthalpy

The amount of heat absorbed or released during a reaction or process under constant pressure.

Exothermic

Releasing heat to the surroundings.

Fire piston

A fire-starting device that burns tinder by rapidly compressing a gas.

First Law of Thermodynamics

Energy can never be created or destroyed. The total energy in the universe is constant.

Heat

The transfer of thermal energy between a system and its surroundings.

Heat of fusion

The amount of heat needed to melt one mole of a substance.

Heat of vaporization

The amount of heat needed to boil one mole of a substance.

Hess's Law

The change in enthalpy of a reaction (ΔH) is the same if the reaction happens in a single step or in a series of steps. Thus, the series of steps must have individual enthalpy changes that add up to the total change in enthalpy for the process

Internal energy

The sum total of all different types of energy in a system (thermal, chemical, etc.).

Joule

The International System of Units (SI) unit of energy, equal to one newton-meter.

Kinetic energy

The energy of an object due to its motion.

Potential energy

The energy of an object due to its position.

Pressure-volume work

Work done on or by a system due to compression or expansion of gases.

Surroundings

The area outside the boundaries of the system being studied.

System

The part of the universe being studied.

Thermal energy

The energy in a system that relates to the temperature of the system.

Thermochemistry

The study of energy in chemical reactions.

Velocity

The rate of change of the position of an object.

Vis viva

Latin for "living force." Vis viva was the precursor to the modern concept of kinetic energy.

Work

The way a system exchanges energy with the surroundings, excluding heat transfers (pressure-volume work, electrical work, etc.).